Appear as frequently isolated, well-circumscribed, circinate or ovoid dusky red or purple lesions on the skin or mucous membranes (especially of the genitals) and reappear at the same sites each time the drug is taken

Appear as areas of dermatitis or gray-blue hyperpigmentation (phenothiazines and minocyclineSome Brand NamesMINOCINClick for Drug Monograph) on skin exposed to the sun or other ultraviolet light source

Appear as frequently isolated, well-circumscribed, circinate or ovoid dusky red or purple lesions on the skin or mucous membranes (especially of the genitals) and reappear at the same sites each time the drug is taken

Appear as areas of dermatitis or gray-blue hyperpigmentation (phenothiazines and minocyclineSome Brand NamesMINOCINClick for Drug Monograph) on skin exposed to the sun or other ultraviolet light source

Diagnosis

Clinical evaluation and drug exposure history

Sometimes skin biopsy

A detailed history is often required for diagnosis, including recent use of OTC drugs. Because the reaction may not occur until several days or even weeks after first exposure to the drug, it is important to consider all new drugs and not only the one that has been most recently started. No laboratory tests reliably aid diagnosis, although biopsy of affected skin is often suggestive. Sensitivity can be definitively established only by rechallenge with the drug, which may be hazardous and unethical in patients who have had severe reactions.

Treatment

Discontinuation of offending drug

Sometimes antihistamines and corticosteroids

Most drug reactions resolve when drugs are stopped and require no further therapy. Whenever possible, chemically unrelated compounds should be substituted for suspect drugs. If no substitute drug is available and if the reaction is a mild one, it might be necessary to continue the treatment under careful watch despite the reaction. Pruritus can be controlled with antihistamines and topical corticosteroids. For IgE-mediated reactions (eg, urticaria), desensitization (see Desensitization) can be considered when there is critical need for a drug.

When progression from urticaria to anaphylaxis is a concern, treatment is with aqueous epinephrineSome Brand NamesADRENALINClick for Drug Monograph (1:1000) 0.2 mL sc or IM and with the slower-acting but more persistent soluble hydrocortisone 100 mg IV, which may be followed by an oral corticosteroid for a short period (see also Treatment).

Key Points

Because drugs can cause a wide variety of reactions, drugs should be considered as causes of almost any unexplained skin reaction.

Base the diagnosis primarily on clinical criteria, including a detailed history of prescription and OTC drugs.

Stop the suspected offending drug and treat symptoms as needed.

Last full review/revision November 2013 by Wingfield E. Rehmus, MD, MPH